Lesser known areas of the Palazzo Ducale, including the original Prigioni Vecchie (Old Prisons), can be visited on the Itinerari Segreti (Secret Itineraries) tour. Book tickets ahead for the tour at the Palazzo Ducale ticket desk or online.
The 1½-hour tour is an intriguing look at the underside of the palace and the workings of government in the days of La Serenissima.
You are first taken through some administrative offices, small timber-clad rooms in which the Republic's civil servants beavered away. These employees were often wealthy citizens but never nobles. They mostly went unpaid (to serve the state was an honour), although their chief, the Cancellier Grande (like the doge, elected for life), received more than 3000 ducats a year (about around €50,000 a month in today's coin).
Adjoining the Cancelleria (Chancellery), where 24 public servants spent their days writing three or four copies of the state's documents, treaties and the like (no photocopiers in those days!), was the Camera del Tormento, a torture room that started business in the evening when the human photocopiers went home for the day. Three judges, the Signori della Notti (Night Lords), would interrogate prisoners here, while others waited in the darkness of cells, terrified by the screams of the torture victim. To be fair to the Venetians, it appears physical torture did not feature high on the Serenissima's justice system. The last known case of torture here dates to 1660 and Venice was the first European state to abolish torture in the 18th century.
Up some narrow stairs you reach Piombi (Leads), prison cells beneath the roof of the building; prisoners froze in winter and sweltered in summer. Giacomo Casanova got five years here for his apparently wayward lifestyle (although many suspect that as a spy for the Republic, he was actually locked up because he had some embarrassing information). The guide will show you how he made his escape (according to his own account). You also get an explanation of the engineering behind the ceiling of the immense Sala del Maggior Consiglio below. The forest of tough larch-wood beams that holds up the immense ceiling without the help of pillars was made by workers from the Arsenale when Antonio da Ponte directed the Palazzo Ducale's rebuilding after the 1577 fire. They haven't been touched since.
You then get to pass the Sala dei Tre Capi del Consiglio dei Dieci (Room of the Three Heads of the Council of Ten), judges who would question those who had left denunciations in the bocche della verità (mouth of truth) distributed around the city. In 1386 it became obligatory to sign such denunciations with two witnesses. Denunciations could be made for any crime, from tax evasion to matters of state. If accusers were found to have fabricated the accusation, they were punished with the penalty that would have been applied to the accused. In this way, citizens were encouraged to think twice before making light-hearted accusations.
The toughest prisoners ended up in the Pozzi (Wells), two bottom storeys of dank cells at (but, contrary to popular belief, not below) water level. They are closed to the public, but from all accounts, by the rather dismal standards of the Middle Ages, they could have been worse.